Breast cancer represents a significant health problem. More than 180,000 new cases are diagnosed, and nearly 45,000 women die of the disease each year in the United States.
The clinical goal of breast imaging is to detect tumor masses when they are as small as possible, preferably less than 10 mm in diameter. It is reported that women with mammographically detected, 1-10 mm invasive breast carcinoma have a 93% 16-year survival rate.
Conventional screen film mammography is the most effective tool for the early detection of breast cancer currently available. However, mammography has relatively low sensitivity to detect small breast cancers (under several millimeters). Specificity and the positive predictive value of mammography remain limited owing to an overlap in the appearances of benign and malignant lesions. Limited sensitivity and specificity in breast cancer detection of mammography are due to its poor contrast detectability, which is common for all types of projection imaging techniques (projection imaging can only have up to 10% contrast detectability). The sensitivity with which conventional mammography can identify malignant tumors in the pre-clinical phase will largely be affected by the nature of the surrounding breast parenchyma. Detection of calcifications will be influenced to a lesser degree by the surrounding tissue. The perception of breast masses without associated calcification, representing the majority of tumors in patients with detected carcinomas, is greatly influenced by the mammographic parenchymal pattern. Thus conventional mammography is often not able to directly detect tumors of a few millimeters due to poor low contrast resolution. Conventional mammography requires ultrahigh resolution (50-100 xcexcm/pixel) to image microcalcifications to compensate for its poor contrast resolution. Mammography fails to initially demonstrate 30%-35% of cancers. In addition, not all breast cancers detected with mammography will be found early enough to cure. At best, it appears that conventional mammography can reduce the death rate by up to 50%. This is an important gain, but there is considerable room for improvement in early detection of breast cancer.
Relatively low specificity of mammography results in biopsy for indeterminate cases despite the disadvantages of higher cost and the stress it imposes on patients. There is a need for more accurate characterization of breast lesions in order to reduce the biopsy rate and false-positive rate of biopsy.
There are several radiological or biological characteristics of breast carcinoma that can be imaged. First, carcinoma has different x-ray linear attenuation coefficients from surrounding tissues, as shown in FIG. 1. Second, carcinoma has a substantially higher volume growth rate compared to a benign tumor, which lacks growth. Third, carcinoma has patterns distinguishable from those of a benign tumor. Fourth, benign tumors show no contrast enhancement after intravenous contrast injection. Fifth, the presence of neovascularity can indicate cancer. Conventional mammography relies mainly on the first characteristic and partially uses the third characteristic for breast cancer detection. Since mammography is a two-dimensional static imaging technique, it cannot provide any information regarding characteristics 2, 4, or 5.
Currently, radiological evaluation of breast cancer is important not only for early detection of disease, but also for staging and monitoring response to treatment. So far, conventional screen film mammography has been shown to be the most cost-effective tool for the early detection of breast cancer. The specificity and positive predictive value of mammography, however, remain limited, owing to an overlap in the appearances of benign and malignant lesions and to poor contrast detectability, which is common for all projection imaging techniques. Projection imaging can have only up to 10% contrast detectability. Biopsy is therefore often necessary in indeterminate cases, despite the disadvantages of higher cost and the stress it imposes on patients. There is therefore a need for more accurate characterization of breast lesions in order to reduce the biopsy rate.
In the last decade, MRI of the breast has gained a role in clarifying indeterminate cases after mammography and/or ultrasound, especially after breast surgery and in detecting multifocal breast cancers. However, the integration of MR into routine clinical practice has been hampered by a number of limitations, including long scanning times and the high cost of MR examinations. Additionally, many patients cannot undergo MR because of MR contraindications (e.g., aneurysm clips, pacemaker) or serious claustrophobia.
Characterization of breast lesions on MR has been based largely on the differential rates of enhancement between benign and malignant lesions. The constant trade-off between spatial and temporal resolution in MR has made it difficult to achieve the spatial resolution necessary for improved lesion characterization.
Standard fan beam computed tomography (CT), including spiral CT, has been evaluated as a potential tool for the characterization of breast lesions. Most previous work has been based on the traditional or helical technique using the whole body scanner. That technique, however, suffers from a number of disadvantages including significantly increased radiation exposure due to the fact that standard CT can not be used to target only the breast, so that the majority of x-rays are wasted on whole body scanning. That leads to relatively low in-plane spatial resolution (typically 1.0 lp/mm), even lower through plane resolution (less than or equal to 0.5 lp/mm in the direction perpendicular to slices), and prolonged volume scanning times, since spiral CT scans the whole volume slice by slice and takes 120 seconds for the whole breast scan. It still takes 15-30 seconds for the latest multi-ring spiral CT for 1 mm/slice and 12 cm coverage.
Ultrasound has poor resolution in characterizing lesion margins and identifying microcalcifications. Ultrasound is also extremely operator dependent.
In addition, for conventional mammography, compression is essential for better low-contrast detectability. However, patients are uncomfortable even though compression may not be harmful to them.
It will be readily apparent from the foregoing that a need exists in the art for a mammography imaging system and method which overcome the above-noted limitations of conventional techniques.
It is therefore a primary object of the invention to provide a clinically useful three-dimensional mammography technique for accurate detection of breast cancer.
It is another object of the invention to provide a mammography technique which can operate with only a single fast volume scanning to provide true three-dimensional (3D) description of breast anatomy with high isotropic spatial resolution and lesion location, while conventional mammography only provides two-dimensional projection images.
It is yet another object of the invention to provide imaging technique to tomographically isolate a breast tumor from the other objects in adjacent planes, consequently eliminate overlap and remove superimposed structures.
It is yet another object of the invention to provide higher contrast resolution compared with conventional mammography and adequate spatial resolution for breast cancer detection.
It is yet another object of the invention to improve the detectability of breast carcinoma (tumors) of a few millimeters in size due to much better low contrast resolution, compared to conventional mammography.
It is yet another object of the invention to provide high resolution volume of interest (VOI) reconstruction mode for target imaging and better characterization of breast tumors three-dimensionally compared with conventional mammography.
It is yet another object of the invention to provide a three-dimensional tomographic reconstruction technique to detect the difference of x-ray linear attenuation coefficients of carcinoma from surrounding tissue. (carcinoma has different x-ray linear attenuation coefficients from surrounding tissue.)
It is yet another object of the invention to provide accurate depiction of breast tumor border pattern for better characterization of breast tumors compared with conventional mammography (carcinoma has distinguishable border patterns from those of a benign tumor).
It is yet another object of the invention to improve specificity in breast cancer detection compared with conventional mammography by allowing more precise measurement of change in lesion volume over relatively short periods of time (carcinoma has a much faster volume growth rate than a benign tumor).
It is yet another object of the invention to provide a mammography technique usable with intravenous (IV) injection of iodine contrast to improve detection and characterization of breast tumors by allowing an assessment of lesion vascularity and enhancement rate (a benign tumor and a malignant tumor have different contrast enhancement rates).
It is yet another object of the invention to provide a mammography technique usable with intravenous (IV) injection of iodine contrast to assess breast tumor angiogenesis non-invasively.
It is yet another object of the invention to increase patient comfort by decreasing the amount of breast compression required.
It is yet another object of the invention to use CBVCTM image-based volume growth measurement technique (both positive growth and negative growth) to determine malignancy of breast tumors and to monitor the effect of breast cancer treatment (this method can be also used for other malignancies, such as lung cancer).
It is yet another object of the invention to use higher x-ray energies than those used in conventional mammography, for breast imaging to increase penetration, improve image quality and reduce patient radiation dose.
It is yet another object of the invention to perform multi-resolution volume tomographic reconstruction from the same set of projection images to improve the dectectibility of microcacification and breast carcinoma (tumors), better characterize breast tumors, and consequently reduce the total accumulative dose for patient.
It is yet another object of the invention to use a CBVCTM image-based computer aided diagnostic technique to improve the detectibility and characterization of breast carcinoma (tumors).
It is yet another object of the invention to improve sensitivity of breast cancer detection and thereby further reduce mortality of breast cancer by detecting small breast cancers that can not be detected by conventional mammography.
It is yet another object of the invention to improve specificity of mammography and greatly reduce the biopsy rate.
It is yet another object of the invention to provide adequate image quality for the mammographically dense breast.
It is yet another object of the invention to facilitate 3D image-guided biopsy procedures.
It is yet another object of the invention to allow accurate assessment of cancer extent for both better pre-surgical planning, especially in limited resections, and radiation therapy treatment planning, as well as for more accurate monitoring of breast cancer response to treatments.
To achieve the above and other objects, the present invention is directed to a system and method incorporating a cone beam volume tomographic reconstruction technique with the recently developed flat panel detector to achieve cone beam volume computed tomographic mammography (CBVCTM). With a cone beam geometry and a flat panel detector, a flat panel-based cone beam volume computed tomography mammography (CBVCTM) imaging system can be constructed, and three-dimensional (3D) reconstructions of a breast from a single fast volume scan can be obtained. In contrast to conventional mammography, the flat panel-based CBVCTM system can provide the ability to tomographically isolate an object of interest (e.g., a lesion) from an object (e.g., other lesion or calcification) in adjacent planes. The 3D tomographic reconstructions eliminate lesion overlap and provide a complete, true 3D description of the breast anatomy. In contrast to existing computed tomography (CT) with an intraslice resolution of 1.0 lp/mm and through plane resolution of 0.5 lp/mm, the CBVCTM reconstructions can have 2.0 lp/mm or better of isotropic spatial resolution (or, more generally, better than 1 lp/mm) along all three axes. The invention is further directed to an ultrahigh resolution volume of interest (VOI) reconstruction using the zoom mode of the flat panel detector to achieve up to 5.0 lp/mm resolution. Thus, CBVCTM can have many times better contrast detectability (tomographic imaging can have up to 0.1% contrast detectability) than that of conventional mammography.
Various scanning geometries can be used. It is contemplated that either a circle scan or a circle-plus-line (CPL) scan will be used, depending on the size of the breast. However, other geometries, such as spiral, can be used instead.
The present invention provides better detection of breast cancers, better lesion characterization, and more accurate preoperative and postoperative information on breast anatomy, thus reducing the negative biopsy rate.
The present imaging technique has significant clinical impact on breast cancer detection, diagnosis and the evaluation of the effectiveness of therapy. Because of its excellent low contrast detectability and high and isotropic resolution, the present invention significantly improves the accuracy of breast lesion detection, and hence greatly reduces the biopsy rate. The potential clinical applications of such a modality are in the imaging of the mammographically indeterminate lesions, the mammographically dense breast and the post-surgical breast. Currently, most mammographically indeterminate lesions end up being biopsied in order to arrive at a definitive diagnosis. It is well known that the usefulness of mammography in patients with dense breasts is limited and that additional imaging or biopsy is frequently required. The use of an imaging modality that has a capability for multiplanar and volumetric data acquisition has the potential to improve lesion characterization in dense breast tissue. The higher spatial resolution afforded CBVCTM can potentially improve the differentiation of recurrence and form of post-surgical changes.
The present invention provides very high-resolution tomographic images by zooming in on small lesions or specific regions within a tumor. Detailed interrogation of specific areas within a lesion, e.g., microcalcifications, necrotic and cystic as well as areas of intraductal extension enables more accurate characterization of breast lesions. The use of contrast material and dynamic imaging provides additional temporal information, which, together with morphological features, enhances specificity and reduces the biopsy rate.
Tumor angiogenesis is an independent prognostic indicator in breast cancer. Currently, angiogenesis is determined by assessing microvessel density in pathologic specimens. However, researchers have also detected good correlation between contrast enhancement and microvessel density. The use of contrast medium in an imaging modality that provides very high spatial and temporal resolution offers a non-invasive method to assess tumor angiogenesis. Additionally, the acquisition of volumetric data with 3D rendering allows multiplanar imaging and better presurgical planning, especially in limited resections.
In summary, the introduction of CBVCTM, with the potential for obtaining a very high spatial resolution tomographic images, offers improved lesion characterization in mammographically indeterminate breast lesions with a view to reducing the biopsy rate. It also offers the advantages of enhancing preoperative and postoperative planning.
CBVCTM has the capacity to provide information regarding characteristics 1-5 discussed above with reference to the prior art to improve lesion detection and characterization.
In a preferred embodiment, the patient lies face down on an ergonomic patient table having one or two breast holes. The gantry holding the x-ray source and the flat panel detector rotates below the table to image the breast or two breasts. To obtain projections other than simple circle projections, the gantry frame can be moved vertically, or the table can be moved vertically. One advantage of having two breast holes is to preserve the geometric relationship between the breasts. In an alternative embodiment, the patient stands before the gantry with straps to hold the patient still.
A further modification of the present invention uses an ultra-high-resolution volume-of-interest (VOI) reconstruction mode to focus on a suspicious lesion. The ultra-high-resolution VOI reconstruction mode is analogous to magnified mammography.
CBVCTM will provide very high-resolution tomographic images by zooming in on small lesions or specific regions within a tumor. Detailed interrogation of specific areas within a lesion (i.e. microcalcifications, necrosis and cysts as well as areas of intraductal extension without overlap structures) will enable more accurate characterization of breast lesions.
CBVCTM will potentially provide a non-invasive method to assess tumor angiogenesis. Recent work has established that tumor angiogenesis is an independent prognostic indicator in breast cancer. Currently, angiogenesis is determined by assessing microvessel density in pathologic specimens. However, researchers have also detected good correlation between contrast enhancement and microvessel density. The use of contrast media in an imaging modality that provides very high spatial and temporal resolution may offer a non-invasive method to assess tumor angiogenesis.
With the present invention, a CBVCTM scan can be completed rapidly, and several sets of scans can be performed continuously for dynamic contrast studies and angiogenesis studies.
Throughout the specification and claims, it will be understood that the present invention is not limited to mammography, but should instead be understood as broadly applicable to breast imaging in general.